Fuel reforming apparatus

ABSTRACT

A fuel reforming apparatus for reforming a mixture of fuel and gas containing oxygen includes an air-fuel mixing chamber into which fuel and air are supplied in such a manner that the fuel and the air are mixed with each other; a reforming reaction chamber which is provided downstream of the air-fuel mixing chamber, and which includes a reforming catalyst for reforming the mixture; and a mixture flow chamber which is provided between the air-fuel mixing chamber and the reforming reaction chamber. The cross sectional area of an outlet of the air-fuel mixing chamber is smaller than the cross sectional area of an inlet of the reforming reaction chamber. An inner wall surface of the mixture flow chamber is formed such that the outlet of the air-fuel mixing chamber is smoothly continuous with the inlet of the reforming reaction chamber.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2003-382992 filed on Nov. 12, 2003, including the specification, drawings, and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel reforming apparatus for reforming a mixture of fuel and gas containing oxygen.

2. Description of the Related Art

An internal combustion engine is known, in which a fuel reforming apparatus including a reforming catalyst is provided, and a fuel component obtained by reforming various types of fuel using the fuel reforming apparatus is burned in a combustion chamber, whereby stable combustion is obtained, and amounts of HC and NOx in exhaust gas are reduced (for example, refer to Japanese Patent Laid-Open Publication No. 2001-241365 (JP-A-2001-241365)). A typical fuel reforming apparatus that can be applied to such an internal combustion engine includes a reforming catalyst for reforming a mixture of fuel and air, and a mixing chamber that is provided upstream of the reforming catalyst (for example, refer to Japanese Patent Laid-Open Publication No. 2001-227419 (JP-A-2001-227419)). A fuel injection valve for supplying fuel into the mixing chamber, and an air supply pipe for supplying air into the mixing chamber are connected to the mixing chamber. Also, a fuel injection apparatus is known, in which a swirl flow of air can be generated around fuel injected from a nozzle hole of a nozzle for injecting fuel so that atomization of fuel and mixing of fuel and air can be promoted (for example, refer to Japanese Utility Model Laid-Open Publication No.5-57356 (JP-U-5-57356)).

However, in the aforementioned fuel reforming apparatus, there is a possibility that the fuel and the air that are supplied into the mixing chamber are not mixed uniformly, and the concentration of the mixture that flows from the mixing chamber into the reforming reaction chamber becomes non-uniform. Therefore, it is not easy to allow a reforming reaction in the reforming reaction chamber to proceed efficiently so as to obtain desired reforming efficiency.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a fuel reforming apparatus which allows fuel and gas containing oxygen to be mixed with each other uniformly, and which has high reforming efficiency.

A first aspect of the invention relates to a fuel reforming apparatus for reforming a mixture of fuel and gas containing oxygen. The fuel reforming apparatus include a mixing chamber into which fuel and gas containing oxygen are supplied, and a reforming reaction chamber which is provided downstream of the mixing chamber, and which includes a reforming catalyst for reforming the mixture. Further, a cross sectional area of an outlet of the mixing chamber is smaller than a cross sectional area of an inlet of the reforming reaction chamber.

In the fuel reforming apparatus, the fuel and the gas containing oxygen are supplied into the mixing chamber having the outlet whose cross sectional area is smaller than the cross sectional area of the inlet of the reforming reaction chamber in such a manner that the fuel and the gas containing oxygen are mixed with each other. With the configuration, the fuel is atomized efficiently in the mixing chamber in which a flow rate is increased, and the fuel reliably contacts the gas containing oxygen in the mixing chamber. Accordingly, in the fuel reforming apparatus, the fuel and the gas containing oxygen can be mixed with each other uniformly. Thus, it is possible to allow the reforming reaction in the reforming reaction chamber to proceed efficiently, and to obtain high reforming efficiency.

A second aspect of the invention relates to a fuel reforming apparatus for reforming a mixture of fuel and gas containing oxygen. The fuel reforming apparatus include a mixing chamber; fuel supply means for supplying fuel to the mixing chamber; gas supply means for supplying gas containing oxygen to the mixing chamber; and a reforming reaction chamber which is provided downstream of the mixing chamber, and which includes a reforming catalyst for reforming the mixture. Further, a cross sectional area of an outlet of the mixing chamber is smaller than a cross sectional area of an inlet of the reforming reaction chamber.

The gas containing oxygen may be air or exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic diagram showing a configuration of a fuel reforming apparatus according to an embodiment of the invention;

FIG. 2 is an enlarged partial cross sectional view showing a main portion of the fuel reforming apparatus shown in FIG. 1;

FIG. 3 is a cross sectional view showing a nozzle member included in the fuel reforming apparatus shown in FIG. 1; and

FIG. 4 is a partial cross sectional view showing a fuel reforming apparatus according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a configuration of a fuel reforming apparatus according to an embodiment of the invention. A fuel reforming apparatus 1 shown in FIG. 1 can reform a mixture of air and hydrocarbon fuel such as gasoline. For example, the fuel reforming apparatus 1 is used for generating fuel (reformate gas) for an internal combustion engine that is a driving source of an automobile. As shown in FIG. 1, the fuel reforming apparatus 1 includes a main body 2 that is formed to have a generally cylindrical shape, and an injector (fuel supply means) 3 connected to an end portion of the main body 2 (an end portion on the right side in FIG. 1).

The injector 3 is connected to a fuel tank (not shown) via a fuel supply pipe L1 and a fuel pump (not shown). When the fuel reforming apparatus 1 is used, the injector 3 injects hydrocarbon fuel such as gasoline. As shown in FIG. 2, the injector 3 is housed in an injector housing portion 4 that is connected to the main body 2 of the fuel reforming apparatus 1. In the injector housing portion 4, an annular air chamber 40 is formed so as to surround a fuel injection hole 3 a of the injector 3. An end of an air supply pipe L2 including an air pump AP and a flow amount adjusting valve FCV is connected to the injector housing portion 4 such that the air supply pipe L2 communicates with the air chamber 40. When the fuel reforming apparatus 1 is applied to an internal combustion engine, an exhaust gas recirculation pipe may be connected to the air supply pipe L2 (at a portion downstream of the flow amount adjusting valve FCV) in order to introduce exhaust gas of the internal combustion engine to the fuel reforming apparatus 1, as shown in FIG. 1. The exhaust gas recirculation pipe is connected to an exhaust pipe of the internal combustion engine. Also, only the exhaust gas may be introduced into the air chamber 40 without introducing air (outside air) into the air chamber 40 via the air supply pipe L2.

A nozzle member 5 is connected to an end of the injector 3. The nozzle member 5 includes an air-fuel mixing chamber 50 which is provided in a center of the nozzle member 5 so as to extend in an axial direction. The air-fuel mixing chamber 50 is a space having a small capacity and having a circular cross section. The air-fuel mixing chamber 50 has an inner diameter that is smaller than an inner diameter of the main body 2 (for example, the air-fuel mixing chamber 50 has the inner diameter that is approximately 5 to 15% of the inner diameter of the main body 2). The air-fuel mixing chamber 50 communicates with the fuel injection hole 3 a of the injector 3, and the inside of the main body 2 of the fuel reforming apparatus 1. Further, plural air injection holes 51 which allow the air-fuel mixing chamber 50 and the aforementioned air chamber 40 to communicate with each other are provided in the nozzle member 5. O-rings for preventing the fuel or air from leaking to the outside are provided between the injector housing portion 4 and the injector 3, and between the injector housing portion 4 and the nozzle member 5.

In the embodiment, each of the air injection holes 51 is formed so as to extend from an outer periphery of the air-fuel mixing chamber 50 to a center of the air-fuel mixing chamber 50, and to be displaced from the center by a predetermined length in a predetermined direction. With the configuration, the air flowing from the air chamber 40 to the air-fuel mixing chamber 50 (and the mixture) are swirled around an axis of the nozzle member 5 in the air-fuel mixing chamber 50. That is, each of the air injection holes 51 of the nozzle member 5 introduces air to a portion around the fuel injection hole 3 a of the injector 3. In addition, each of the air injection holes 51 functions as swirl flow generating means for generating a swirl flow of the mixture in the air-fuel mixing chamber 50. Also, the air injection hole 51 may be formed so as to have the shape of spiral starting from the center of the air-fuel mixing chamber 50. In this case as well, the air injection hole 51 functions as the swirl flow generating means for generating a swirl flow in the air-fuel mixing chamber 50. Also, the air injection holes 51 may be formed so as to radiate in a radial direction in the nozzle member 5. In this case, the air injection holes 51 do not function as the swirl flow generating means for generating a swirl flow in the air-fuel mixing chamber 50.

Meanwhile, in the main body 2, a reforming reaction chamber 7 including a predetermined reforming catalyst is provided at a predetermined interval from the injector housing portion 4. A mixture flow chamber 6 that communicates with the air-fuel mixing chamber 50 is formed between the injector housing portion 4 and the reforming reaction chamber 7. The capacity of the mixture flow chamber 6 is larger than the capacity of the air-fuel mixing chamber 50 of the nozzle member 5. The total length of the mixture flow chamber 6 (i.e., the length of the mixture flow chamber 6 in the axial direction of the main body 2) is set considering the capacity of the air-fuel mixing chamber 50, the cross sectional area of an outlet of the air-fuel mixing chamber 50, and further a range in which the fuel is sprayed by the injector 3. In the embodiment, an inner wall surface 6 a of the mixture flow chamber 6 is formed to be a curved surface such that the inner diameter of the mixture flow chamber 6 gradually increases from the air-fuel mixing chamber 50 to the reforming reaction chamber 7, and the outlet of the air-fuel mixing chamber 50 is smoothly continuous with an inlet of the reforming reaction chamber 7, as shown in FIG. 2.

Also, in the embodiment, the reforming reaction chamber 7 is configured by disposing honeycomb body supporting a predetermined reforming catalyst in the main body 2. In the embodiment, the honeycomb body has an outer diameter that is substantially equal to the inner diameter of the main body 2. With the configuration, the cross sectional are of the inlet of the reforming reaction chamber 7 is larger than the cross sectional area of the outlet of the air-fuel mixing chamber 50 of the nozzle member 5. As the reforming catalyst included in the reforming reaction chamber 7, for example, a catalyst in which rhodium is supported by zirconia is employed. Further, a reformate gas supply chamber 8 is formed downstream of the reforming reaction chamber 7 of the main body 2. A reformate gas supply pipe L3 (refer to FIG. 1) for supplying reformate gas to a target component such as an internal combustion engine is connected to the reformate gas supply chamber 8.

The fuel reforming apparatus 1 includes an electronic control unit (hereinafter, referred to as “ECU”) 10 that functions as control means for the fuel reforming apparatus 1, as shown in FIG. 1. The ECU 10 includes a CPU, ROM, RAM, an input/output port, a storage device, and the like (none of them are shown in the figure). The injector 3, the air pump AP, and the flow amount adjusting valve FCV, various sensors, and the like are connected to the input/output port of the ECU 10. The EUC 10 controls the injector 3, the air pump AP, the flow amount adjusting valve FCV, and the like based on detection values of the various sensors according to various control programs, maps, and the like.

When the mixture of fuel and air is reformed using the fuel reforming apparatus 1 thus configured, the ECU 10 of the fuel reforming apparatus 1 controls at least one of the injector 3, the air pump AP, and the flow amount adjusting valve FCV such that the air-fuel ratio of the mixture supplied to the reforming reaction chamber 7 becomes a desired value based on the signals from the various sensors according to a predetermined map or the like. In the embodiment, the desired value is a generally constant value. For example, a ratio O/C between the number of carbon atoms in the fuel supplied to the air-fuel mixing chamber 50 and the number of oxygen atoms in the air supplied to the air-fuel mixing chamber 50 is set to be in a range of approximately 0.8 to 1.05). Thus, the injector 3 injects the fuel into the air-fuel mixing chamber 50. Also, the air supply pipe L2 supplies air into the air chamber 40 in the injector housing portion 4. The air that has flown into the air chamber 40 is injected from each of the air injection holes 51 of the nozzle member 5 into the air-fuel mixing chamber 50 such that the air collides with the fuel injected from the injector 3. Further, a swirl flow is generated due to the air (and the mixture) in the air-fuel mixing chamber 50.

Thus, in the fuel reforming apparatus 1, the fuel and the air are supplied to the air-fuel mixing chamber 50 in such a manner that the fuel and the air are mixed with each other. The air-fuel mixing chamber 50 has the outlet whose cross sectional area is smaller than the cross sectional area of the inlet of the reforming reaction chamber 7, and has the capacity smaller than the capacity of the mixture flow chamber 6. With the configuration, the fuel is atomized efficiently in the air-fuel mixing chamber 50 in which the flow rate is increased, and the fuel reliably contacts the air in the air-fuel mixing chamber 50 which is a small space. Accordingly, in the fuel reforming apparatus 1, the fuel and the air can be mixed with each other uniformly. Thus, it is possible to allow the reforming reaction in the reforming reaction chamber 7 to proceed efficiently, and to obtain high reforming efficiency (high fuel conversion rate). Also, in the fuel reforming apparatus 1, since the swirl flow is generated in the air-fuel mixing chamber 50 due to the air flowing into the air-fuel mixing chamber 50 from each of the air injection holes 51 (and the mixture) as described above, the fuel and the air are mixed with each other in the air-fuel mixing chamber 50 more uniformly.

The mixture of fuel and air, which is obtained by mixing the fuel and the air uniformly in the air-fuel mixing chamber 50, flows into the mixture flow chamber 6 from the air-fuel mixing chamber 50. Since the inner wall surface 6 a of the mixture flow chamber 6 is formed such that the outlet of the air-fuel mixing chamber 50 is smoothly continuous with the inlet of the reforming reaction chamber 7, the mixture obtained by mixing the fuel and the air uniformly in the air-fuel mixing chamber 50 flows into the mixture flow chamber 6 from the air-fuel mixing chamber 50, and flows in the mixture flow chamber 6 while being diffused along the inner wall surface 6 a of the mixture flow chamber 6. Then, the mixture flows into the reforming reaction chamber 7 from the mixture flow chamber 6. As a result, in the fuel reforming apparatus 1, it is possible to reliably prevent the concentration of the mixture in the mixture flow chamber 6 from becoming non-uniform.

Subsequently, in the reforming reaction chamber 7, the hydrocarbon fuel and the air are caused to react with each other by the reforming catalyst. For example, a partial oxidation reaction that is represented by the following formula (1) proceeds, whereby the reformate gas containing CO and H₂ is generated. The obtained reformate gas flows into the reformate gas supply chamber 8 from the reforming reaction chamber 7. Then, the reformate gas is supplied to the target component such as the internal combustion engine from the reformate gas supply chamber 8. C_(m)H_(n)+(m/2)O₂→mCO+(n/2)H₂   (1)

In the embodiment, supply of air to the air-fuel mixing chamber 50 via the air supply pipe L2, and injection of fuel into the air-fuel mixing chamber 50 by the injector 3 are controlled by the ECU 10 separately. With the configuration, the air-fuel ratio of the mixture supplied to the reforming reaction chamber 7 can be set freely according to an operating condition of an internal combustion engine to which the fuel reforming apparatus 1 is applied, a state of the reforming catalyst in the reforming reaction chamber 7, and the like. Also, when the fuel reforming apparatus 1 is applied to an internal combustion engine, air can be inhaled into the air-fuel mixing chamber 50 using vacuum pressure in the combustion chamber of the internal combustion engine. Therefore, in this case, the air pump AP may be omitted.

Further, in order to start the reforming reaction in the reforming reaction chamber 7, it is necessary to make the temperature of the reforming reaction chamber 7 (reforming catalyst) equal to or higher than a predetermined temperature (for example, approximately 400° C.), in addition to supplying the mixture appropriately. In order to make the temperature of the reforming reaction chamber 7 equal to or higher than the predetermined temperature, it is preferable to preheat the reforming catalyst before the reforming reaction is started, by employing a method using a known electrically heated catalyst (not shown) (a method in which electricity is supplied to a so-called metal honeycomb body that is a carrier for supporting the reforming catalyst, which is composed of a metal thin film so as to heat the honeycomb body), a burner type heating method (a method in which a burner is disposed upstream of the reforming catalyst, and the reforming catalyst is heated using heat generated by the burner), or the like. Once the reforming reaction is started, the reforming reaction continues due to heat generated by the reforming reaction. Therefore, supply of electricity to the honeycomb body or heating by the burner may be stopped.

FIG. 4 is a partial cross sectional view showing a fuel reforming apparatus according to another embodiment of the invention. A fuel reforming apparatus 1A shown in FIG. 4 includes a reforming reaction chamber 7A including a reforming catalyst (for example, a catalyst in which rhodium is supported by zirconia). In the reforming reaction chamber 7A, steam reforming is performed using hydrocarbon fuel such as methanol, air, and water so as to obtain predetermined fuel gas. In this case, the fuel reforming apparatus 1A includes a fuel injector 3F, and a water injector 3W. Each of the fuel injector 3F and the water injector 3W injects fuel or water into an air-fuel mixing chamber 50A that is a small space formed in an injector housing portion 4A. The air-fuel mixing chamber 50A has an outlet whose cross sectional area is smaller than the cross sectional area of an inlet of the reforming reaction chamber 7A. Also, in the injector housing portion 4A, an air chamber 40A is formed so as to surround a fluid injection hole of the fuel injector 3F and a fluid injection hole of the water injector 3W. The air chamber 40A communicates with the air-fuel mixing chamber 50A via plural air injection holes 51A.

In the fuel reforming apparatus 1A thus configured as well, the fuel and water are atomized efficiently in the air-fuel mixing chamber 50A in which the flow rate is increased, and the fuel reliably contacts the air in the air-fuel mixing chamber 50A. Accordingly, in the fuel reforming apparatus 1A as well, the fuel, water, and air can be mixed with each other uniformly. Thus, it is possible to allow the reforming reaction in the reforming reaction chamber 7A to proceed efficiently, and to obtain high reforming efficiency. That is, the invention can be applied to a fuel reforming apparatus that includes plural fluid injection means including at least a fuel injection valve. 

1. A fuel reforming apparatus for reforming a mixture of fuel and gas containing oxygen, comprising: a mixing chamber into which fuel and gas containing oxygen are supplied; and a reforming reaction chamber which is provided downstream of the mixing chamber, and which includes a reforming catalyst for reforming the mixture, wherein a cross sectional area of an outlet of the mixing chamber is smaller than a cross sectional area of an inlet of the reforming reaction chamber.
 2. The fuel reforming apparatus according to claim 1, wherein air is supplied to the mixing chamber, as the gas containing oxygen.
 3. The fuel reforming apparatus according to claim 2, further comprising: an air supply pipe for supplying the air to the mixing chamber; and a gas supply pipe, wherein the fuel reforming apparatus is provided in a vehicle including an internal combustion engine; the gas supply pipe is connected to the air supply pipe and an exhaust pipe of the internal combustion engine; and exhaust gas of the internal combustion engine is supplied to the mixing chamber via the gas supply pipe, as the gas containing oxygen.
 4. The fuel reforming apparatus according to claim 1, further comprising: a mixture flow chamber that is provided between the mixing chamber and the reforming reaction chamber, wherein an inner wall surface of the mixture flow chamber is formed such that the outlet of the mixing chamber is smoothly continuous with the inlet of the reforming reaction chamber.
 5. The fuel reforming apparatus according to claim 4, wherein the mixing chamber has a capacity that is smaller than a capacity of the mixture flow chamber.
 6. The fuel reforming apparatus according to claim 1, further comprising: swirl flow generating portion that generates a swirl flow of the mixture in the mixing chamber.
 7. The fuel reforming apparatus according to claim 1, wherein each of the mixing chamber and the reforming reaction chamber has a circular cross section.
 8. The fuel reforming apparatus according to claim 7, wherein the mixing chamber has a circular cross section whose inner diameter is 5 to 15% of an inner diameter of the inlet of the reforming reaction chamber.
 9. The fuel reforming apparatus according to claim 1, further comprising: a fluid injection valve that supplies a fluid used for a reforming reaction to the mixing chamber.
 10. The fuel reforming apparatus according to claim 9, wherein the liquid injection valve injects water, as the fluid.
 11. A fuel reforming apparatus for reforming a mixture of fuel and gas containing oxygen, comprising: a mixing chamber; fuel supply means for supplying fuel to the mixing chamber; gas supply means for supplying gas containing oxygen to the mixing chamber; and a reforming reaction chamber which is provided downstream of the mixing chamber, and which includes a reforming catalyst for reforming a mixture of the supplied fuel and the supplied gas, wherein a cross sectional area of an outlet of the mixing chamber is smaller than a cross sectional area of an inlet of the reforming reaction chamber.
 12. The fuel reforming apparatus according to claim 11, further comprising: swirl flow generating means for generating a swirl flow of the mixture in the mixing chamber. 